For me, mainly through time.
I've always read. I took a class where Descartes Meditations was assigned. I looked up and it had been an hour and I'd read three pages. A couple of years spent reading philosophy later, and I could read three academic articles in an evening.
In the late 80's I read Eco's Name of the Rose. Two years ago, I reread it. It was a different book.
The same is true for technical books, articles, papers. As I read more of them, I understand more of some of them. And now that I know that, I don't worry deeply about what I don't understand most of the time. It's only when deep knowledge is relevant to something I'm actually doing that I drill down. It's the 'T-shaped' idea. Reading for breadth makes it more likely that I drill down in a productive well.
As for glazing over, I'll do that frequently with equations...happened last night on two pages worth. I went back and looked again and got about all I cared to get.
tl;dr Just keep reading.
